If you waited until the last minute to try and find some solar filters for the annular solar eclipse or transit of Venus, you may have waited too long. As a favor to someone overseas who I will join for the transit, I was trying to find some material to construct simple solar filters for 10" and 12" telescopes, but could not locate any with ease.
After much asking around, I contacted High Point Scientific and they reported a few sheets left. With luck, they will arrive before we depart for the transit.
Joe Cali has written an excellent tutorial of how to construct a solar filter mount using thin solar filter film. Using foam board for large telescopes may be a bit excessive - I suspect we will use cardboard or what ever we can find on board the ship - and duct (gaffer) tape - the astronomer's best friend when it comes to securing filters to the tube.